My favourite is Ilford IT-8
IT-8 Ilford Pyrocatechin Toner
For Olive Black tones.
Stock A
Potassium Bichromate 50 g
Water to 1 litre
Stock B
Hydrochloric Acid (conc) 100ml
Water to 1 litre
Expose and process your print as normal and wash well.
Make up bleach from: 2 parts A and 10 parts B with 40 parts water, bleach the print then wash until all the yellow from the bichromate has been removed from the highlights then redevelop in the following Developer.
Developer
Pyrocatechin 1.75 g
Sodium Carbonate (anhyd) 5 g
Water to 1 litre
Temperature is not critical, it should take 1½ to 2 mins at 20°C, this developer will oxide very quickly and should be discarded when it turns a bluish green.
Wash the print and dry.
While originally fomulated for Ilford Plastika paper I first used this about 30 years ago with Iford Multigrade paper and it does produce lovely warm olive tones.
Print - Forte Polywarmtone FB, Developed in ID-78, right half toned in IT-8
This was posted in the Chems section but seems to have been lost.
Ian